Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$61.86	10.600%	$68.4172	$68.42	$68.40	$68.40
Purchase #2	$170.86	11.663%	$190.7874	$190.79	$190.80	$190.80
Purchase #3	$133.78	4.449%	$139.7319	$139.73	$139.75	$139.70
Purchase #4	$68.58	9.219%	$74.9024	$74.90	$74.90	$74.90
Purchase #5	$90.83	9.123%	$99.1164	$99.12	$99.10	$99.10
Purchase #6	$40.90	13.636%	$46.4771	$46.48	$46.50	$46.50
Purchase #7	$200.44	9.613%	$219.7083	$219.71	$219.70	$219.70
7 purchase totals =	$767.25		$839.1407	$839.15	$839.15	$839.10